Method of and means for forming bellows



Sept. 4, 1956 M. F. PETERS METHOD OF AND MEANS FOR FORMING BELLOWS Filed Dec. 13, 1950 INVENTOR. MEZV/ZZE F Pen-"25 ATTORNEY METHOD OF AND lVIEANS FOR FORMING BELLOWS Melville F. Peters, East Orange, N. J.

Application December 13, 1950, Serial No. 200,561

1 Claim. (Cl. 29-454) This invention provides a method of forming curved surfaces for fluid seals and means to secure the curved surfaces together to form bellows.

In United States patent application, Serial Number 198,079, filed November 29, 1950, by Melville F. Peters, now abandoned, the applicant in this application; described curvature of surface of minimum stress for bellows elements, as the surface formed when a flexible member or membrane is secured or supported by two cylindrical elements and a fluid pressure or its equivalent applied to one side of the membrane, so that the unsupported and unguided area will deform into a curved surface and if the pressure is great enough to exceed the elastic limit of the membrane in the unsupported area, the deformation will continue until the stresses in the membrane are reduced to the yield point.

If the curved surface of bellows elements are formed at a pressure It]? and n=1, the stresses in the elements in the rest position when subjected to a pressure P, is approximately equal to the yield strength of the material and if the bellows is oscillated through an amplitude of :tX when subjected to the forming pressure, the stresses caused in the membrane by the oscillations must be algebraically added to the yield strength of the material. During the life of the bellows the curvature of the surface will change so as to accommodate itself to the greatest stress, but unless the bellows is subjected to conditions which will increase the curvature of the surface, the flexing life of the bellows will be short.

If the formed element is annealed and subjected to the forming pressure, there will be a small increase in curvatures because the yield point of the material is slightly lower in the annealed condition. This process of subjecting the membrane to the forming pressure and annealing may be repeated many times with a small increase in curvature, but at a decreasing rate of increasing curvature for each cycle. The same limiting curvature could have been obtained in one operation by making n slightly greater than 1.

If n is greater than 1 and, for the sake of illustration, is equal to 10, the stresses in the annealed membrane will be approximately ten percent of the yield strength, since the stress S in a membrane subjected to a pressure P, is

S=KP, where K is a complicated function of the physical dimensions and properties of the membrane. If the membrane is oscillated through an amplitude iX, the stresses developed in the membrane will be added algebraically to ten percent of the yield strength, so that by controlling the amplitude of oscillation the annealed membranestwill operate well within the elastic limit.

The surface formed by the pressure nP is not actually the surface of minimum stress for a pressure nP, because the deformation of the membrane stopped when the yield point of the material was reached, and therefore indiffers from the real curvature of a surface having minimum stress by an amount which is proportional to the modulus of elasticity of the membrane material, and approaches the true shape as the modulus of elasticity 2,761,206 Patented Sept. 4, 1956 approaches zero. The true surface shape for each depth of curvature may be photographed or observed by applying fluid pressure to a soap or rubber film secured by its edges to appropriate forms. The surface shape or curvature may then be transferred to a die and flexible members stamped in the conventional manner.

it is an object of this invention to eliminate this procedure by providing a method for forming the curvature of membrane surfaces bounded by two other surfaces or areas, by applying a uniform pressure of 111 over the confined surface, and after securing the membranes together by means of the bounding areas to form a bellows, to limit the working pressure of the bellows to a fluid pressure P. For all practical purposes the fiber stress in the curved surface of a membrane formed with n greater than one, will be the same as the fiber stress in a membrane with the curvature copied from the soap film, when both surfaces have the same depth of curvature and the working pressure does not exceed P. The curvature of the surface is controlled by the forming fluid pressure nP, so that by assigning a series of values to :11, a family of surfaces having'minimum stress are obtained with the same fixture, and the forming fluid pressure required is determined by the working pressure P, the yield strength of the membrane material and the convexity or concavity of the surface subjected to the working pressure in the bellows.

Another object of the invention is to provide a method for forming the curvature of membrance surfaces by applying a fluid pressure of nP over an unsupported portion of the membrane until equilibrium is established between the forming pressure, the yield strength of the material and the thickness of the membrane, so that adjustment in curvature for non-uniformity of material thickness and composition is realized during the forming process, and two areas which serve as supports for the membrane during the forming process, are means for securing the membranes together to form a bellows. i It is a further object of the invention to provide a method of forming the curved surface with a fixture that changes the width of the curved surface throughout its perimeter, so that the moment of inertia of the formed surface is not constant throughout the perimeter, and thereby provide means for limiting the fiber stress in the regions of the surface where the ambient conditions lead to great shearing forces and large bending moments.

It is an object of the invention to provide a method of forming the curved surface with a fixture that permits changes in the width of one or both of the two bounding areas throughout the perimeter and thereby provide means for limiting the fiber stress in the regions of the surface where the ambient conditions lead to great shearing forces and large bending moments.

It is also an object of the invention to provide a method of forming diaphragms by supporting the outer area of a membrane and applying a fluid pressure to the central portion, thus causing the unsupported and unguided portion to deform until equilibrium is reached between the curvature of the deformed surface and the forming pressure.

I It is an object of the invention to provide a method for forming surfaces of curvature of minimum stressby applying a greater pressure than the forming pressure 11F and limiting the deformation to that of a membrane subjected to a forming pressure nP, by means of a limiting device.

Other objects and advantages of this invention relating to the arrangement and operation of the forming elements and economies of manufacture will be apparent to those skilled in the art upon consideration of the description, drawings and appended claims.

In the drawings:

Figure 1 is a cross sectional view of a curvature of a surface having minimum stress and an arc of a circle, an embodiment of the invention herein.

Figure 2 is a cross sectional view of a bellows embodying features of the invention.

Figure 3a and 3b are cross sectional views of a membrane or bellows element forming fixture, embodying features of the invention.

Referring to the drawing and first to Figure l, the curve 1 is the cross sectional view of the surface defined as a curvature of surface of minimum stress and is formed by subjecting an unsupported portion of the membrane to a fluid pressure which stresses the membrane beyond the yield point of the material, and 2 is the cross sectional view of an arc of a circle having the same depth of curvature as 1. The areas or edges 3 and 4 bounding the curved surface 1, provide means for securing the curved surfaces together to form a bellows. The tangent to the fluid formed membrane 1 is parallel to a line tangent to the two areas or edges 3 and 4 at X1 and the tangent to the arc of the circle 2 is parallel to the same line at X2, where X1 and X2 are measured from the axis 13 of the membrane. The distance X2 is greater than X1.

Figure 2 is the cross sectional view of a bellows having surfaces of minimum stress 1, formed by supporting the areas or edges 3 and 4 and applying the pressure nP to the unsupported and unguided surface 1, and the surfaces of minimum stress 1 by supporting the areas or edges 3' and 4' and applying the pressure nP to the unsupported and unguided surface 1, and n is greater than n if the working pressure is to be applied to the convex side of 1 and the concave side of 1', and less if the Working pressure is to be applied to the concave side of 1 and the convex side of 1, and equal to n when the working pressures are low. The curved surface 1 and 1' are prevented from touching during compression of the bellows by forming surface 1 with the support for area or edge 4 shorter and having a greater diameter than for forming surface 1 and the support for area or edge 3 has a greater diameter when surface 1 is formed than when surface 1' is formed, and the difference in diameter be tween the supports 3 and 4 shall be the same for forming both surfaces 1 and 1'. The greatest diameter of the mating area 3 must be equal to the greatest diameter of its mating area 3' and in like manner the mating area 3" must equal 3" and the minimum diameter of the mating area 4 must be equal to the minimum diameter of its mating area 4 and in like manner the mating area 4" must equal 4" and the greatest diameter 3, 3' need not equal the greatest diameter of 3", 3" or the smallest diameter 4, 4 need not equal the smallest diameter 4", 4/).

In Figure 3a the fixture has an upper chamber member 5, with a holding and sealing surface 9, a support 7, and a vent 11 and a conventional triggering unit 12 to release the forming pressure when the membrane has been deflected a predetermined amount, and the lower chamber member 6 with a holding and sealing surface which matches 9, and a means 8 for admitting and returning the fluid used for membrane forming purposes. The membrane is held and sealed between jaws 9 and 1t and the forming pressure applied, until equilibrium is established between the curvature of the surface, the yield strength of the material, and the forming pressure nP. The process can be carried out in two or more steps by applying a pressure nP to bring the central portion of the membrane in contact with support 7, annealing and then continue the process by applying the pressure 11F to form surface 1 with said support still in place. Referring to Figure 3b and 3a, the surface'l is formed after replacing support 7 with support 7, and seals 9 and 10, with seals 9' and. 10', and applying the forming pressure nP to a portion of a membrane which is surrounded by inner and outer peripheral areas which mate with similar peripheral areas of the membrane having surface 1. The bellows elements and bellows shown in Figure 2, having the line 14 tangent to the mating areas 3, and bisecting the distance of separation of areas 4, 4 or 4, 4 has the support 7' equal in length to support 7 plus the separation distance between two adjacent areas 4, 4 or 4, 4', and has a smaller diameter than 7 by twice the thickness of the metal, and th inner diameter of 9 land 10', equal to the inner diameter of 9 and 10 minus twice the thickness of the material, so that the width of formed surface 1 equals the width of formed surface 1'. To secure areas or edges 3 and 4, which bound the formed surface to cylindrical members, support 7 is replaced by a support which is long enough to touch the unformed membrane and the membranes are formed in pairs, half at the pressure nP and the other half at the pressure nP. To form diaphragms the support 7 is removed and the forming pressure n1 is applied until the deformation ceases.

An alternative procedure in applying the forming pressure is to apply a pressure greater than the forming pressure 12F and have a conventional triggering devic 12 release the pressure at the instant the forming of the surface is complete.

The outer and inner peripheries of the bellows element are stamped or cut by conventional methods.

Although the embodiment of the invention has been shown and described in detail herein, it is to be expressly understood that various changes in shape, design and procedure may be made therein without departing from the spirit of the invention as Well understood by those skilled in the art.

I claim:

The process of forming a bellows, which comprises the steps of forming the membranes from flat sheet material by direct contact of fluid pressure of a magnitude to stress the material beyond its elastic limit and greater than the operating pressure of the bellows in a die apparatus in which the central portions of the membranes are supported by axial supports to prevent spherical curvature thereof and the outer annular portions are held in fixed position, the intermediate unsupported annular portions between said central and outer portions of the finished membranes being deformed to different degrees by reason of differences in the diameters and lengths of said axial supports, forming a hole in the central portion of each deformed membrane, assembling the membranes coaxially so that the adjacent membranes have a different degree of deformation and the alternate membranes are the same with the curved intermediate portions of all the membranes extending in the same axial direction thereby preventing said curved intermediate portions from touching during actual use of the bellows, and securing together against leakage the inner and outer peripheries of the adjacent membranes.

References Cited in the file of this patent UNITED STATES PATENTS 1,561,312 Cutler et al Nov. 10, 1925 1,625,914 Seibt Apr. 26, 1927 1,717,196 Emmet Jan. 11, 1929 1,763,582 Gulick June 10, 1930 1,786,506 Ray Dec. 20, 1930 2,522,915 Woods Sept. 19, 1950 FOREIGN PATENTS 465,103 Germany Sept. 5, 1928 387,902 Great Britain Feb. 16, 1933 430,321 Great Britain Nov. 13, 1934 

